A wire electrode of the abovementioned type is known from Offenlegungsschrift No. 31 45 907 (Corresponds to U.S. Pat. No. 4,448,655), in which the surface has projections and recesses. This irregular surface is obtained either through sandblasting or grooving, or, however, also by pulling the wire through a rotating matrix form. Moreover, it is known from this reference to make the surface rough by etching or coats of powder. A particularly advantageous solution is seen in interweaving several wires with one another or, however, in winding a thinner wire onto a thicker carrying wire. The producing of a surface which has recesses by means of a rotating matrix form cannot be carried out for economical reasons, since the wire would have to be advanced at a relatively slow speed, while the matrix form would have to be rotated extremely quickly. Of concern in regard to the other methods for deforming the surface of an eroding wire is that one obtains only irregular surfaces with grooving and sand blasting, which surfaces as a rule are not well suited to remove the eroded material which has accumulated in the cutting gap from the gap. Of concern in regard to the winding of a thin wire onto a thick carrying core, just like the twisting of several thin wires with one another, there exists here on the one hand the disadvantage that this method is relatively expensive from an economics point of view, especially since here the thin wires must have a considerably smaller diameter than the diameter of the eroding wire. The manufacture of thin wires, however, is very complicated and expensive. Moreover, the twisting of the wires with one another and also the winding of a thin wire onto a thicker core is also relatively expensive. However, the main disadvantage is noticeable during eroding. The thin wires have a tendency to burn through first which has the result that the ends stay and rest directly on the workpiece which is to be cut. This results in the eroding wire burning to ashes on the workpiece which is to be cut and thus causing the cutting operation to be interrupted. The eroding wire thus must then be threaded in again and the cutting operation must be started anew.
The basic purpose of the invention is to manufacture an eroding wire of the abovementioned type in an economical manner so that it is provided with such a surface suited to quickly and safely remove the eroded material from the cutting gap and which in spite of this continues to have a high strength and a good electric conductivity.
An inventively constructed eroding wire is thus manufactured of wire having a polygonal cross section. The cross section can be triangular or, however, also square or rectangular. It is also conceivable to use a cross section having more than four corners. This cross-sectional shape of the eroding wire can be obtained in a simple manner by rolling a round wire. The wire is thereafter twisted so that the corners of the wire run helically on same. A rectangular wire has proven to be most advantageous in view of a large cavity inside of the peripheral surface of the wire. An eroding wire according to the invention thus maintains its full cross section, so that its strength and electric-conducting capability is not influenced by creating an irregular surface. Moreover, the helical deformation of the wire has proven to be extremely effective for guiding the eroded material out of the cutting gap, so that the cutting performance was able to be increased considerably. Moreover, the wire electrode has on all sides the same flexibility, which is a condition for a constant cutting performance.
An inventive wire electrode thus works according to the principle of the socalled conveyor worm and transports the dielectric which contains many cut particles at the wire electrode speed out of the narrow working gap.
The lateral free spaces and the surface enlargement of the wire electrode permit a quick discharge of the cut particles and feed always nonused dielectric liquid to the gap. With this the flushing operations are enormously strengthened and much higher removal rates are achieved.
Furthermore, a profiling of the wire electrode creates self-stability, which stability, also due to the favorable water-pressure principles in the working gap, results in a lesser enlargement of the eroding surface of the workpiece.